System and Method for Forming Cavities

ABSTRACT

A technique facilitates forming cavities, e.g. perforations, into a geological formation. A jetting tool is moved downhole into a borehole, and an abrasive fluid is pumped down through the jetting tool. The abrasive fluid is discharged under pressure through a plurality of jetting nozzles to form jets of the abrasive fluid which act against a surrounding wall, e.g. a casing or other borehole wall. The jetting nozzles, and thus the jets, are oriented such that a rebound effect of the jets does not detrimentally impact the jetting tool. Consequently, the jets can be used to cut perforations through the surrounding wall and into the formation without eroding or otherwise detrimentally affecting components of the jetting tool.

CROSS-REFERENCE TO RELATED APPLICATION

The present document is based on and claims priority to U.S. ProvisionalApplication Ser. No. 61/908,687, filed Nov. 25, 2013, incorporatedherein by reference.

BACKGROUND

A variety of perforating techniques and fracturing techniques areconducted in wellbores drilled in geological formations. The resultingperforations and/or fractures facilitate flow of desired fluids throughthe formation and into a wellbore. For example, the production potentialof an oil or gas well may be increased by improving the flowability ofhydrocarbon-based fluids through the formation and into the wellbore. Insome applications, however, difficulties arise in initiating andachieving desirable perforations and fractures to facilitate fluid flow.

SUMMARY

In general, the present disclosure provides a system and method forforming cavities, e.g. perforations, into a geological formation. Ajetting tool is moved downhole into a borehole, and an abrasive fluid ispumped down through the jetting tool. The abrasive fluid is dischargedunder pressure through a plurality of jetting nozzles to form jets ofthe abrasive fluid which act against a surrounding wall, e.g. a casingor other borehole wall. The jetting nozzles, and thus the jets, areoriented such that a rebound effect of the jets does not detrimentallyimpact the jetting tool. Consequently, the jets can be used to cutperforations through the surrounding wall and into the formation withouteroding or otherwise detrimentally affecting components of the jettingtool.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain embodiments will hereafter be described with reference to theaccompanying drawings, wherein like reference numerals denote likeelements. It should be understood, however, that the accompanyingfigures illustrate various implementations described herein and are notmeant to limit the scope of various technologies described herein, and:

FIG. 1 is a schematic illustration of an example of a jetting tooldeployed downhole into a borehole via a conveyance, according to anembodiment of the disclosure;

FIG. 2 is a cross-sectional illustration of an example of the jettingtool showing an angling of the jetting nozzles to avoid erosive reboundeffects, according to an embodiment of the disclosure;

FIG. 3 is a schematic illustration of the jetting tool illustrated inFIG. 1 as operated during a clean out procedure, according to anembodiment of the disclosure;

FIG. 4 is a schematic illustration of an example of jetting nozzleconfiguration for forming desired jets of abrasive fluid, according toan embodiment of the disclosure; and

FIG. 5 is a schematic illustration of another example of the jettingtool, according to an embodiment of the disclosure.

DETAILED DESCRIPTION

In the following description, numerous details are set forth to providean understanding of some illustrative embodiments of the presentdisclosure. However, it will be understood by those of ordinary skill inthe art that the system and/or methodology may be practiced withoutthese details and that numerous variations or modifications from thedescribed embodiments may be possible.

The disclosure herein generally relates to a methodology and system forforming cavities, e.g. perforations, into a geological formation.According to an embodiment, a jetting tool is moved downhole into aborehole, such as a wellbore. An abrasive fluid is pumped down throughthe jetting tool. For example, a surface pumping system for pumpingabrasive jetting fluid may be used to deliver the abrasive fluid downthrough a tubing, e.g. coiled tubing, to an internal flow passage of thejetting tool. From the internal flow passage, the abrasive fluid isdischarged under pressure through a plurality of jetting nozzles to formjets of the abrasive fluid. The jets act against a surrounding wall,e.g. a casing or other borehole wall. To avoid erosive effects withrespect to the jetting tool, the jetting nozzles, and thus the jets, areoriented such that a rebound effect of the jets does not detrimentallyimpact the jetting tool. Consequently, the jets can be used to cutperforations through the surrounding wall and into the formation withouteroding or otherwise detrimentally affecting components of the jettingtool.

The system and methodology are generally related to well site equipment,such as oil field surface equipment, downhole assemblies, coiled tubingassemblies, and other well related equipment. The jetting tool describedherein may be used with many types of well site equipment for a varietyof cavity forming operations. However, the jetting tool also may beutilized with various other types of equipment and in otherapplications, e.g. non-well related applications. In some wellapplications, the jetting tool is used to direct a stream of abrasivefluid from a tubing interior, such as a coiled tubing interior, througha nozzle or nozzles formed in the jetting tool, and outwardly toward awellbore casing to create resulting cavities, e.g. perforations.

According to an embodiment, a jetting tool is run downhole into awellbore, i.e. run in hole, via coiled tubing or another suitableconveyance. The coiled tubing is used to adjust the depth of the jettingtool to a desired depth at which a first set of perforations is to beformed. An abrasive slurry or similar fluid is then pumped downholethrough the coiled tubing, through the jetting tool, and out through thejetting nozzles to perforate a surrounding borehole wall. For example,the jets of abrasive fluid/slurry may be used to perforate a casing andthen to further perforate into the surrounding formation a sufficientdistance to enable communication of hydraulic pressure into theformation, e.g. into an oil or gas bearing formation.

Once the first set of perforations is formed, the jetting tool may berepositioned at a suitable distance away from the newly formedperforations. The distance from the first set of perforations isselected to ensure the coiled tubing tool string is far enough away fromthe first set of perforations so that the tool string does not get stuckduring a fracturing procedure. A hydraulic fracture slurry is thenpumped downhole through an annular space between the coiled tubing andthe surrounding casing and out into the perforations. The hydraulicfracture slurry is sufficiently pressurized to fracture the formationwhich has just been perforated.

Excess hydraulic fracture slurry tends to settle and accumulate abovethe zone that has just been fractured, and this excess slurry is cleanedout and returned to the surface in a clean out operation. By way ofexample, the clean out operation may be performed by running the jettingtool back downhole while reverse circulating clean fluid. The cleanfluid is reverse circulated from the surface, down through the annulus,in through the jetting nozzles (and/or other suitable passages), and upthrough an interior of the coiled tubing to a surface collectionlocation. In some embodiments, a reverse circulation check valve, e.g.ball check valve, may be used in cooperation with the jetting nozzles ofthe abrasive jetting tool to facilitate the clean out operation.

After cleaning out the excess fracture slurry, the jetting tool may berepositioned to another perforation depth or location within thewellbore. At the subsequent perforation depth, another set of cavities,e.g. perforations, may be created through the surrounding casing andinto the formation. The perforations are then used for a fracturingoperation followed by a reverse circulating clean out operation, asdescribed above. This process of perforating, fracturing, and cleaningout excess fracturing slurry may be repeated a desired number of timesto form multiple sets of perforations according to the parameters of agiven operation.

During a clean out operation, a consideration for an operator of theabrasive jetting tool is the rate of penetration (ROP) which is definedas penetrated distance of the clean out operation divided by the time ofthe clean out operation. The ROP is affected by how well the settledslurry may be stirred up and sent flowing back up through the interiorof the coiled tubing.

With conventional perforation formation, bottom hole assemblies (BHAs)are not able to direct jets downwardly. Additionally, conventional BHAssuffer from erosion of components, such as erosion of nozzles. Withconventional BHAs, the injected abrasive fluid rebounds or reflects backfrom the surrounding wall and/or from newly formed perforations, thusimpacting the bottom hole assembly. The abrasive fluid often containssolid particles which erode material from the BHA, including removal ofmaterial from an exterior surface of the tool body. Additionally, therebound effect can result in the abrasive fluid impacting the nozzlesinjecting the fluid, thus causing rapid wear of the nozzles anddeterioration of the perforating operation.

Referring generally to FIG. 1, an example of a cavity forming orperforating system 20 is illustrated. In this embodiment, perforatingsystem 20 comprises a jetting tool 22 having a tool body 24. The jettingtool 22 may be conveyed into a borehole 26, e.g. a wellbore, by asuitable conveyance 28, such as coiled tubing 30. By way of example, thejetting tool 22 may be directly coupled with coiled tubing 30 via acoiled tubing connector 31. The jetting tool 22 may be connected withcoiled tubing connector 31 via threaded engagement or other suitableengagement techniques.

In many applications, the borehole 26 is in the form of a wellboredrilled into a geological formation 32, such as a hydrocarbon fluidbearing formation. In such applications, the jetting tool 22 may be usedto facilitate the production of hydrocarbon fluids, e.g. oil and/or gas,from the formation 32. The wellbore 26 may be lined with a suitablecasing 34 which provides a surrounding wellbore wall 36 into which thejetting tool 22 is deployed. However, the surrounding wellbore wall 36may comprise an open borehole or various other materials and/or featureslining the borehole 26.

The production of hydrocarbon fluids may be facilitated by formingcavities 38, e.g. perforations, through the casing 34 and into theformation 32. The perforations 38 also may be used to facilitatefracturing operations which effectively fracture the formation 32 tofurther facilitate the flow of hydrocarbon fluids to the wellbore 26 forproduction to a suitable collection location.

In a perforating operation, the jetting tool 22 is moved downhole intowellbore 26 to a desired location for forming perforations 38. Anabrasive fluid is then pumped down through a flow passage 40 of jettingtool 22 and out through a plurality of jetting nozzles 42. As thepumped, abrasive fluid flows out through jetting nozzles 42 underpressure, jets 44 are formed and act against the surrounding wellborewall 36, e.g. against casing 34, to form perforations 38 through thecasing 34 and into the formation 32. By way of example, the flow passage40 may extend longitudinally along an interior of tool body 24 and maybe aligned with, e.g. concentric with, a longitudinal, central axis 46of jetting tool 22 (see also FIG. 2).

In some applications, the abrasive fluid is pumped down along aninterior 48 of coiled tubing 30, down through the jetting tool 22 viaflow passage 40, and out through at least one, e.g. a plurality, ofjetting nozzles 42. The outflow through jetting nozzles 42 forms jets 44of the abrasive fluid which act against the surrounding wellbore wall36. In this example, the jetting tool 22 may be coupled directly to thecoiled tubing 30 such that a fluid may be pumped from the interior 48 ofcoiled tubing 30 and immediately into the flow passage 40 of jettingtool 22, i.e. without passage through other components. Additionally,the jetting nozzles 42, and thus the jets 44, are oriented at an anglewith respect to axis 46 such that a rebound effect of the jets 44 doesnot detrimentally impact the jetting tool 22.

For example, the jetting nozzles 42 may be oriented such that arebounded or reflected portion 50 of the abrasive fluid rebounds orreflects in a direction which misses the jetting tool 22, as illustratedin FIG. 1. Thus, the rebound effect of abrasive fluid bouncing off ofthe surrounding wellbore wall 36 during a perforating operation does notsubstantially impact the jetting tool 22, and thus does not causeerosion of the jetting nozzles 42 or of other portions of jetting tool22. This enables the use jets 44 under desired pressures and flow ratesto form the desired perforations 38 without detrimentally affectingoperation of the jetting tool 22 over time. In a variety of wellapplications, the jets 44 facilitate formation of perforations 38 farenough into formation 32 to enable communication of hydraulic pressureinto the oil or gas bearing formation 32 during, for example, afracturing procedure.

Referring again to FIG. 2, the desired rebound effect of jets 44 may beachieved by orienting each jetting nozzle 42, and thus each jet 44, at asuitable angle with respect to axis 46. In an embodiment, each jettingnozzle 42 of a plurality of jetting nozzles 42 is oriented to form anacute angle 52 with the axis 46 of between about 55 degrees and about 75degrees. In some applications, the acute angle 52 between each jettingnozzle 42 and the jetting tool axis 46 may be approximately 65 degrees.The acute angle 52 is measured between axis 46 and a nozzle axis 54 of acorresponding jetting nozzle 42. In some applications, the acute angle50 may be different for each jetting nozzle 42, but the acute angle 52also may be the same or similar for each jetting nozzle 42.

In the example illustrated, the acute angle 52 is on the downhole orlead end side of the jetting tool 22. Thus, during a perforatingoperation, the abrasive fluid forms jets 44 which flow outwardly anddownwardly with respect to the jetting tool 22. In this type ofarrangement, the reflected or rebounded portion 50 of abrasive fluid isreflected downwardly ahead of the jetting tool 22 such that the abrasivefluid substantially or entirely misses the jetting tool 22. Asillustrated, the reflected portion 50 may pass ahead of a lead end 55 ofjetting tool 22.

After forming the first set of perforations 38, the jetting tool 22 maybe pulled uphole, via coiled tubing 30, a predetermined distance abovethe previously formed set of perforations 38. A hydraulic fracturingslurry is then pumped down through an annulus 56 between the coiledtubing 30 and the surrounding wellbore wall 36 formed by, for example,casing 34. It should be noted that in some applications, the fracturingslurry may be pumped down along passages other than annulus 56. Thehydraulic fracturing slurry is forced outwardly under pressure intoperforations 38 to fracture the formation 32. Following the fracturingoperation, excess hydraulic fracturing slurry 58 is cleaned out of thewellbore 26 by running the jetting tool 22 back downhole while reversecirculating a clean fluid, as represented by arrow 60 in FIG. 3.

In the embodiment illustrated, the clean fluid 60 is pumped from asurface location, down through the annulus 56, into the jetting tool 22through the plurality of jetting nozzles 42, up through flow passage 40,and up along the interior 48 of coiled tubing 30. The clean fluid 60carries the excess hydraulic fracturing slurry 58 to a collectionlocation at the surface where the hydraulic fracturing slurry 58 may beseparated from the clean fluid 60. The jetting tool 22 may then be movedto another desired location along wellbore 26 so as to form another setof perforations 38 at a different well zone. The process of deployingjetting tool 22, forming a set of perforations 38, fracturing formation32 via the set of perforations 38, cleaning out the excess fracturingslurry, and moving the jetting tool 22 to a subsequent perforationforming location can be repeated a desired number of times for a desirednumber of well zones.

Depending on the application, the jetting tool 22 may comprise a singlejetting nozzle 42 or a plurality of jetting nozzles 42. If a pluralityof jetting nozzles 42 is employed for a given application, the jettingnozzles 42 may vary in number and arrangement. In some applications, thejetting nozzles 42 are spaced equidistant about a circumference of thejetting tool 22, although the jetting nozzles 42 can be staggered orarranged with different circumferential distances and/or longitudinaldistances between sequential jetting nozzles 42. In FIG. 4, a specificexample is illustrated in which the jetting tool 22 comprises threejetting nozzles 42 arranged generally equidistant around thecircumference of jetting tool 22 with approximately 120 degrees betweensequential jetting nozzles 42. However, greater or lesser numbers ofjetting nozzles 42 may be constructed in a variety of arrangements andpatterns with the desired acute angle 52 is selected to reduce oreliminate the rebound impact of abrasive fluid flowed outwardly throughjetting nozzles 42 under pressure.

Referring generally to FIG. 5, another embodiment of jetting tool 22 isillustrated. In this embodiment, the jetting tool 22 comprises a passage62 extending through the tool body 24. In some embodiments, the passage62 may be located at the lead end 55 of jetting tool 22, e.g. alignedwith the central axis 46 of jetting tool 22. By way of example, thepassage 62 may cooperate with a check valve 64 which acts against acorresponding seat 66 to allow upward flow of fluid, e.g. clean fluid,as represented by arrows 68. However, the check valve 64 blocks outwardflow of fluid from internal flow passage 40 to the surrounding wellbore26. In the embodiment illustrated, the check valve 64 comprises a ball70 sized to seal against seat 66 during, for example, an injectionoperation in which fluid flows outwardly through the plurality ofjetting nozzles 42.

Without passage 62, the entire flow of returned clean fluid flowsthrough jetting nozzles 42 in a reverse circulation direction during aclean out operation. This action ensures a relatively high flow rate ofcleaning fluid through the jetting nozzles 42 and a rigorous removal ofexcess fracturing slurry 58. Effectively, the rate of penetration can besubstantially improved during the reverse clean out operation byenabling a better pick up of solids from the wellbore 26. However, someapplications may benefit from the added volume of flow facilitated bythe addition of passage 62 and check valve 64. With the addition ofpassage 62 and check valve 64, clean fluid can be reversed circulatedthrough both passage 62 and jetting nozzles 42 during a clean outoperation. With either embodiment, the jetting tool 22 may beconstructed in a substantially shorter and simpler configuration ascompared to conventional jetting tools.

In addition to reducing or eliminating the rebound effect, the angledjetting nozzles 42 also may be used to break up consolidated solids. Forexample, the excess fracturing slurry 58 may comprise sand (and/or othersolids) which tends to consolidate in the wellbore 26. However, thedownhole angle of jetting nozzles 42 enables use of the jetting nozzles42 for directing jets of fluid against the consolidated solids toeffectively chop up the settled sand and/or other solids.

The system and methodology described herein may be employed in non-wellrelated applications which utilize jets for cutting perforations orother types of cavities. Additionally, the overall perforations systemmay comprise a variety of other and/or additional components. Thejetting tool may be conveyed on coiled tubing or another type ofsuitable conveyance. The flow of injection fluid, e.g. flow of anabrasive jetting fluid and/or flow of hydraulic fracturing slurry, maybe directed along an interior of the conveyance or along other suitableflow paths routed downhole along the wellbore. Additionally, variousnumbers, arrangements, and angular orientations of the jetting nozzlesmay be employed depending on the parameters of a given application. Thejetting nozzles 42 also may comprise a variety of inserts, hardenedinserts, coatings, or other features to facilitate creation and controlof jets 44.

As described above, the jetting tool 22 provides a simplifiedconstruction which enables improvement of the rate of penetration duringclean out while providing down jetting capability for improved clean outfunctionality. The jetting tool 22 also reduces tool erosion otherwiseresulting from the rebound effect, thus providing an increased tool lifeand increased jetting time. The simplified construction and erosioncontrol features of the jetting tool also facilitate performance ofjetting operations with a reduced number of additional tool stringcomponents and spare parts. The construction of at least someembodiments further facilitates reverse circulation and clean outoperations due to a reduced number of orifices for reverse fluid flow.This effectively reduces the potential for detrimental issues arisingwhile employing desired rates of penetration during reversesand/proppant clean out.

Although a few embodiments of the system and methodology have beendescribed in detail above, those of ordinary skill in the art willreadily appreciate that many modifications are possible withoutmaterially departing from the teachings of this disclosure. Accordingly,such modifications are intended to be included within the scope of thisdisclosure as defined in the claims.

What is claimed is:
 1. A system for forming perforations in a well,comprising: a coiled tubing; and a jetting tool coupled to the coiledtubing by a coiled tubing connector, the jetting tool having a flowpassage therein which extends along a longitudinal axis of the jettingtool to a plurality of jetting nozzles, thus forming a flow path throughthe flow passage and the plurality of jetting nozzles, the plurality ofjetting nozzles being oriented such that a rebounded portion of fluidflowing out of the plurality of jetting nozzles and against asurrounding wall is directed to miss the jetting tool.
 2. The system asrecited in claim 1, wherein each jetting nozzle of the plurality ofjetting nozzles is oriented to form an acute angle with the longitudinalaxis, the acute angle being between about 55 degrees and about 75degrees.
 3. The system as recited in claim 1, wherein each jettingnozzle of the plurality of jetting nozzles is oriented to form an acuteangle with the longitudinal axis, the acute angle being approximately 65degrees.
 4. The system as recited in claim 1, wherein the jetting toolis coupled directly to the coiled tubing such that a fluid may be pumpedfrom an interior of the coiled tubing and immediately into the flowpassage of the jetting tool.
 5. The system as recited in claim 1,wherein the jetting tool further comprises a seat and a check valvereceived in the seat.
 6. The system as recited in claim 5, wherein thecheck valve comprises a ball which seals against the seat during aninjection operation in which fluid flows outwardly through the pluralityof jetting nozzles.
 7. The system as recited in claim 5, wherein theseat and the check valve are located along the axis of the jetting tool.8. A method, comprising: moving a jetting tool downhole in a wellboredrilled into a formation; pumping an abrasive fluid down through thejetting tool and out through a plurality of jetting nozzles to form jetsof the abrasive fluid which act against a surrounding wall; orientingthe jets such that a rebound effect of the jets does not detrimentallyimpact the jetting tool; and using the jets to cut perforations throughthe surrounding wall.
 9. The method as recited in claim 8, whereinmoving comprises moving the jetting tool downhole via coiled tubing. 10.The method as recited in claim 8, wherein pumping comprises pumping theabrasive fluid down through a flow passage oriented along a longitudinalaxis of the jetting tool and out through the plurality of nozzles. 11.The method as recited in claim 10, wherein orienting the jets comprisesorienting the plurality of jetting nozzles at an acute angle of betweenabout 55 degrees and about 75 degrees with respect to the longitudinalaxis.
 12. The method as recited in claim 10, wherein orienting the jetscomprises orienting the plurality of jetting nozzles at an acute angleof approximately 65 degrees with respect to the longitudinal axis. 13.The method as recited in claim 9, further comprising pulling the jettingtool uphole a predetermined distance from the perforations.
 14. Themethod as recited in claim 13, further comprising pumping a hydraulicfracture slurry down through an annulus between the coiled tubing and asurrounding casing and then into the perforations to fracture theformation.
 15. The method as recited in claim 14, further comprisingcleaning out excess hydraulic fracture slurry by running the jettingtool back downhole while reverse circulating a clean fluid from asurface location down through the annulus, into the jetting tool throughthe plurality of jetting nozzles, and up through an interior of thecoiled tubing.
 16. The method as recited in claim 15, wherein cleaningout further comprises returning a portion of the clean fluid through acheck valve located downhole from the plurality of nozzles.
 17. Themethod as recited in claim 15, wherein cleaning out further comprisesreturning the clean fluid in its entirety through the plurality ofjetting nozzles.
 18. A method, comprising: forming a jetting tool with acentral axis, a flow passage extending along the central axis, and aplurality of jetting nozzles in communication with the flow passage;orienting the plurality of nozzles at an angle with respect to thecentral axis; and selecting the angle such that jets of fluid flowingoutwardly through the plurality of nozzles are directed outwardly andtoward a lead end of the jetting tool.
 19. The method as recited inclaim 18, further comprising moving the jetting tool downhole into awellbore lined with casing; and pumping and abrasive fluid down throughthe flow passage and out through the plurality of jetting nozzles to cutcavities in a surrounding wall.
 20. The method as recited in claim 19,wherein selecting comprises selecting the angle such that a reboundeffect of abrasive fluid rebounding off the surrounding wall does noterode the jetting tool.